1. Field of the Invention
The present invention relates to a light emitting diode (LED) driver device, and more particularly, to an LED driver device providing appropriate response speed, small size, easy fabrication, lower production costs and less noise.
2. Description of the Related Art
LEDs form a plurality of arrays with respect to three colors of red, green and blue, respectively, to be used as a back light of a liquid crystal display (LCD) apparatus.
As shown in FIG. 1, a conventional driver 200 for driving such an LED includes a dimming amount calculator 202 receiving the average luminance (Y) value of a video signal and calculating the dimming controlling amount of respective RGB colors; a modulation controller 206 receiving the dimming controlling amount, receiving information about the RGB colors inputted from a light sensor 204 and outputting a pulse width modulation signal; a signal shifting part 208 generating a reference timing signal having a phase shifted in sequence to sequentially shift the phase of the pulse width modulation signal with respect to each of the RGB LEDs 250; an AND gate 210 receiving the pulse width modulation signal of the modulation controller 206 and the reference timing signal of the signal shifting part 208 and outputting a signal by a logical AND operation thereof; and a plurality of LED drivers 212 receiving an output signal of the AND gate 210 and driving the LED 250.
If the pulse width modulation signal of the modulation controller 206 is simultaneously applied to the plurality of LED drivers 212 in parallel, large current stress is applied to a power source unit. Hence, the LED driver 200 sequentially applies the pulse width modulation signal to each of LED lines or the drivers.
Then, the signal shifting part 208 generates the reference timing signal having phase difference, as much as the number of the drivers, by using a counter 214 and a shift register 216. When the reference timing signal of the signal shifting part 208 and the pulse width modulation signal of the modulation controller 206 are performed with an AND operation by the AND gate 210, the phase of the pulse width modulation signal is sequentially shifted and the drivers 212 are sequentially driven.
The conventional LED driver 200 employs a field-programmable gate array (FPGA) or a complex programmable logic device (CPLD) in the signal shifting part 208 to achieve fast response of high brightness LED, thereby sequentially dimming at high speed.
However, it is required to slow down the response speed of the light sensor 204 and the modulation controller 206 to the range of 100 ms to 500 ms to prevent drastic color change recognized by human's eye. That is, the response speed of the whole system should be slowed down to maintain stable white balance. Further, the high speed response of the LED may cause adverse effects on the LCD back light. Thus, the dimming control at appropriate speed corresponding to a human eye's recognition limit is more effective than the dimming control using high speed digital logic.
Meanwhile, the conventional LED driver 200 utilizes the signal shifting part 208 as a complex additional logic number to supply information on analog dimming, PWM dimming, etc. to each of the drivers in parallel through an analog signal line, thereby requiring many circuit wires.
Also, in the analog signal line corresponding to a low voltage, much noise may be introduced into the circuit when a large current and a high voltage repeatedly fluctuate, thereby leading to malfunction and abnormal oscillation.
Further, as a main controller of the conventional LED driver 200 does not have a function for determining a current value of the LEDs, the malfunction thereof is not automatically detected, and initial current setting for production cannot be automated.